3406c fuel return line size

93 pete 4ck 3406c. any one tell me what size the fuel return line should be. apparently i have number 6 hose on it now but was going to replace the fitting in the injection pump and they gave me one with a number 4 return line hookup and it is restricted. number 6 was on the truck when i bought it and the return line fitting in the injection pump is NOT restricted. any input would be appreciated. thanks

the fitting is a restricted orifice, it is what keeps the fuel pressure up, am surprised you had fuel pressure if you did not have a restricted fitting in the return! On a engine dyno if someone puts a regular fitting in the return you will not get over 10 psi fuel pressure. they do make a fitting with a number 6 fitting.

The elbo on the back of the pump should be a constant feed orfice. You need to go back with whatever came on the engine. If I remember correctly, the orfice was 9 millimeters, just shy of 3/8 which is #6 hose. Check with Cat.....

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One of the last 2 Stroke mechanics left.44 years in the business and worked on everything from 53 series to 149 series. Winding it down now...time to move on.

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